As a psychologist, I’ve always been bothered by the term “common sense.” To me, it indicates a savvy understanding of situations, and an ability to make the most of the situation before you–the best playing of the cards you hold, so to speak.

It has bothered me because you could say that “common sense” just refers to someone who is intelligent. Perhaps that person doesn’t have other qualities we associate with intelligence (a broad vocabulary, wide-ranging knowledge), but they still have a lot of cognitive horsepower. That argument didn’t feel right to me, but I didn’t know how to rebut it.

In a new book What Intelligence Tests Miss (right), psychologist Keith Stanovich offers a way to understand the difference between intelligence and common sense.

Stanovich starts the book by asking us to consider why smart people do dumb things. Take David Denby, film critic for the The New Yorker. With a divorce settlement looming, Denby decided it would be useful to make a million dollars quickly. Although he knew nothing about investing, he sold all of his conservative investment products in late 1999 and bought technology stocks on NASDAQ. Denby reported in his book, American Sucker, that he knew that this move was not rational. Could anyone really “beat the market,” especially someone who knew next to nothing about investing?As his losses mounted, he continued to invest, in a vain attempt to recoup his losses.

How could someone who likely would score very high a standard intelligence test do not just one bone-headed thing, but a whole series of really bone-headed things?

As the book title suggests, Stanovich argues that our conception of “intelligence” is incomplete. Unlike other psychologists (notably Howard Gardner and Robert Sternberg) he does not want to expand the definition of intelligence to expertise in domains such as music, creativity, or interpersonal skills. He wants to stick with a more traditional definition of intelligence: solving problems, making effective decisions, and the like.

Stanovich argues that there are really three components to the cognitive system that handles these functions. First, there is what Stanovich calls the autonomous mind. It engages in thinking based on simple associations; It allows you to do what you have always done in the past, and in fact to feel as though you are on auto-pilot, because the autonomous mind operates very rapidly and effortlessly. For example, when you face 60 types of bread at the supermarket and simply buy the bread that you usually buy, you are using the autonomous mind.

If the bread you usually buy is out of stock, you will be forced to use the algorithmic mind. The algorithmic mind processes information, juggling concepts in working memory, making comparisons among them, combining them in different ways, and so forth. Thus, you might examine different brands of a bread to determine which is most like the one you usually buy in terms of cost and nutritional content.

Intelligence tests measure the efficiency of the algorithmic mind. What they miss is the reflective mind.

The reflective mind refers to the goals of the system, beliefs relevant to these goals, and the selection of actions to try to get to these goals.

Here’s an example of the difference between them. A friend of mine recently selected a daycare for her son. She used the algorithmic mind quite effectively: she weighed various factors, e.g., the financial cost, the seeming warmth of the caretakers, whether the facilities were clean and inviting. But her goal in putting these factors together was short-sighted. She heavily weighted the daycare’s proximity to her house. It was obvious to me (and her other friends) that the philosophy of child-rearing at this daycare did not match hers. After several months of complaining about what the caregivers did and said, she started looking for another daycare.

An intelligence test measures the algorithmic mind, that is, how efficiently my friend weighs the factors. But to make effective decisions and adapt to your environment sensibly, you need to do more. You need to see your environment for what it is, you need to set realistic goals, and you need to select actions that move you towards those goals. That is the job of the reflective mind, and these features are not measured by standard intelligence tests. That’s why smart people do dumb things like send their child to a daycare that will not work out, or try to beat the stock market.

Stanovich does not just tell stories to persuade the reader that the three types of mind differ. He mostly relies on data from laboratory tasks. Psychologists have provided many examples of irrational thinking in the last forty years and Stanovich catalogues them into three classes of errors that the reflective mind makes. I’ll illustrate just one. Try answering this problem.

Jack is looking at Anne but Anne is looking at George. Jack is married, but George is not. Is a married person looking at an unmarried person?

A) Yes B) No C) Cannot be determined.

About 80% of people get this problem wrong, most of them answering C, cannot be determined. The answer to the problem becomes obvious when one considers Anne. If she’s married, then the answer to the problem is “yes” because Anne is looking at George. If she’s not married, then the answer is “yes” because Jack is looking at her.

Why do most people get the problem wrong? It is the autonomous mind leading them astray. They see that the problem does not specify that whether or not Anne is married, and there is an association between the idea “information is missing” and “cannot solve the problem.”

Overriding this associative “answer” provided by the autonomous mind is one of the jobs of the reflective mind. The extent to which people do this varies; some have a bias to do it across situations, and some have a bias not to do it. Stanovich stresses that this tendency to actually think through a problem and not use the autonomous-mind answer is only weakly related to IQ.

That’s the important new idea in the book. Even though both the algorithmic and the reflective mind are important in tasks we associate with intelligence such as successfully solving problems in real world situations, we only consider functions of the algorithmic mind to reflect “intelligence,” and that is all that IQ tests measure.

Stanovich points out that we do very little in schools to nurture the reflective mind. Given that it is important to reaching ones goals, academic or otherwise, perhaps we should. Steve Pinker has suggested that schooling should especially focus on cognitive processes that we deem important, but that the mind does not do well naturally. By that criterion, the reflective mind qualifies for more attention in schools because quite a lot of data show that most of us do not use the it as optimally as we might.

But can common sense be taught? To some extent, yes. With sufficient practice, people can come to recognize the types of errors the reflective mind makes, and learn to avoid them.

What Intelligence Tests Miss is a very useful book indeed, and I highly recommend it.